1. Field of the Invention
The present invention relates to the farming of aquatic crustaceans of the genus "Procambrus" (e.g., Procambrus clarkii), and more particularly relates to a method and apparatus for the growth of premolt crawfish and harvesting of soft shell crawfish during the molt cycle. Even more particularly, the present invention relates to an apparatus and method for the growth of premolt crawfish and harvesting of soft shell crawfish where the crawfish are concentrated and segregated according to the degree of advancement in their molt cycle.
2. General Background
Certain edible freshwater crustacea are known by the genus Procambrus and there are various species.
One particular species known in the southern part of Louisiana is Procambrus clarkii which is known more commonly as the red swamp crawfish. In areas where these crustacea are popular as a food item, they are simply known by the name "crawfish" or by the slang term "crawdads." Another species is the white river crawfish.
Crawfish have for some time been prepared as a food item in certain parts of Louisiana, primarily in the southern portion thereof and primarily by the numerous French speaking descendants of Nova Scotia known as the "Acadians" or "Cajuns".
Crawfish are eaten in a variety of forms including the very popular boiled crawfish as well as certain other more complex delicacies including crawfish bisque (stuffed crawfish in a brown "roux" gravy served over rice), crawfish etoufee (crawfish sauteed in seasoned sauce and served over rice), crawfish pie (crawfish and seasoned vegetables prepared in a pastry shell), fried crawfish tails (crawfish fried in seasoned batter), etc. Many of these and other exotic crawfish dishes are sold in the nationally famous seafood and creole restaurants in the City of New Orleans, La.
Recently, a new delicacy has appeared in fine restaurants in the South Louisiana area, that dish known as "soft shelled crawfish." To oversimplify, the dish is prepared from soft shell crawfish which applies to either newly molted crawfish that are soft or those that have molted twelve to twenty-four hours before and have a flexible parchment-like shell.
Soft shell crawfish as a food item is a recent development. Extensive farming techniques are needed to economically produce soft shell crawfish in sufficient numbers to make it readily available to the consumer. A significant potential exists for soft shell crawfish in the seafood industry. Although the molting physiology behavior per se is known to the academic community, a need exists for the production of large 3-5 inch crawfish in sufficient numbers through an efficient and economical method. It is the purpose of this invention to provide a method and apparatus which when used together will make for an efficient and economical method for producing commercial quantities of soft shell crawfish suitable as a food item.
Rapid-molting small crawfish, in the 1 to 3 inch range, have been produced commercially for the fish bait industry. The intermolt period for small crawfish is shorter than that of larger crawfish. These smaller rapid-molting crawfish are much easier to concentrate and require less holding time before molting than do the larger crawfish.
As the period of holding time is extended, feeding and cannibalism becomes a problem resulting in increased production time and labor. Large premolt crawfish still feeding and placed in open bottom tanks cannot be concentrated in adequate numbers to merit a commercial shedding operation. To hold, feed, and individually collect large crawfish in open bottom tanks or cages would entail prohibitive space requirements, energy and expense, including exhorbent labor costs.
Producing large soft shell crawfish in a shedding operation involves handling each individual crawfish three to eight times. Crawfish can be concentrated in higher numbers in tanks if there is a substrate which increases the actual surface and which would also provide protection and isolation for individual crawfish. However, a random placement and quantity of such a substrate sufficient to concentrate large crawfish in a tank apparatus would pose several problems.
First to consider is that too much substrate would restrict the movement of crawfish and would increase cannibalism since those recently molted or those close to molting would be trapped against the substrate and could not easily escape the more aggressive feeding crawfish. Secondly, indiscriminate substrate configuration, quantity and placement would obscure observation nd would make for obstacles when trying to harvest one particular individual crawfish out of a concentrated population. It has been found that substrate is important and that if arranged in a configuration so as to allow a large open area to remain in the tank, crawfish would concentrate in the substrate when isolation was preferred and would move into the open area when feeding and movement was preferred. Since soft shell and late premolt crawfish avoid any substrate which would tend to entrap them, the juxtoposition of a substrate to an open area is beneficial as it would tend to segregate soft shell and late premolters from the more aggressive population. Although the open area provides some means of segregation, the open area is heavily used by aggressive crawfish and is designated best as feeding area rather than a molting area. Additional and localized segregation of soft and late premolt crawfish is desirable and can be achieved by providing a shallow area in the tank which is separate and distinct from an open feeding area and the substrate area. Segregation is further enhanced when the surface of the shallow molting area is provided with a shape or a texture which retards the walking speed of encroaching aggressive crawfish while at the same time allowing the escape technique of backward locomotion by tail action to remain relatively unimpeaded for the soft or late premolt crawfish. The use of light and dark contrast also adds to the other segregating characteristics to make the apparatus more efficient. This is done by either shading the substrate and feeding area, and/or coloring the apparatus so that the shallow area is light and the open feeding area is dark.
The tank apparatus with its characteristic areas is supplied with optimum quality water in either a recirculating or a flow through system. The intermolt/premolt growth tanks are arranged in an assembly like fashion in close proximity with "stocked seining ponds" and/or holding cages. "Stocked seining ponds" are small ponds constructed to be easily seined or trawled (with little or no bottom substrate or excessive loose vegetation) and being easily cooled or heated by flowing water and/or shading and greenhouse effect. These ponds are stocked with selected crawfish graded to be in the intermolt or premolt phase, fed, held and seined when the collective growth of the majority is anticipated to be approaching the late premolt phase. Stocked seining ponds are maintained so that a reproducing population of crawfish is not present. These crawfish are further graded upon seining--soft ones for market, feeding premolters for intermolt/premolt growth tanks, and late premolters for open bottom molt tanks.
Holding cages in an acceptable supply of water and near to the intermolt/premolt growth tanks make for added convenience as a handy supply source for restocking intermolt/premolt tanks and replacing dead or other crawfish being removed from the intermolt/premolt growth tanks in small numbers.
By using the stocked seining ponds the time frame for crawfish in the intermolt/premolt growth tanks is reduced. A more rapid turnover (production of soft shell crawfish) can be achieved as much of the growth required to reach the late premolt phase occurs in the stocked seining ponds, where the crawfish are captured collectively rather than individually, as they are in the intermolt/premolt growth tanks.
The final stage for molting requires no special features in the molt tanks since crawfish in the late premolt phase are committed to molting and will not feed or cannibalize each other. In this stage they can be concentrated without concern for much other than water quality.